1. Field of the Invention
The present invention relates to dielectric paste and a thick film capacitor using the same and more particularly to dielectric paste useful as a material for forming a load capacitor of a ceramic oscillator and a thick film capacitor using the same.
2. Related Art
A thick film capacitor is being used, for example, as a component of a thick film integrated circuit. As a dielectric substance for such thick film capacitor, one which is mainly composed of barium titanate ceramics and to which a glass component is added as desired is mainly used.
For instance, an example in which BaTiO.sub.3 --CaSnO.sub.3 --CaSiO.sub.3 ceramics is used as the dielectric substance is described in Japanese Patent Laid-Open No. 51-48159 and an example in which BaTiO.sub.3 --(Pb, Sr) (Ti, Sn)O.sub.3 and glass are used as the dielectric substance is described in Japanese Patent Laid-Open No. 51-150097. The thick film capacitor is then obtained by forming a dielectric paste by dispersing powder of the above-mentioned dielectric substance and of glass, as desired, into an organic vehicle, applying it on an insulated substrate such as alumina by means of screen-printing or the like and then by sintering in air.
With the development of digital IC technology, a ceramic oscillator using piezoelectric ceramics has come to be used widely as a reference signal (or clock signal) generating element in electronic equipment. Such a ceramic oscillator is normally connected to a load capacitor which conforms to temperature characteristics of a resonator which is necessary in constructing an oscillating circuit. With the miniaturization of recent electronic equipment, the demand for miniaturization of the electronic parts such as the ceramic oscillator is also increasing.
To that end, a trial using a thick film capacitor, instead of a discrete type capacitor, as a load capacitor to be connected to the ceramic oscillator has made to obtain a built-in capacitor ceramic oscillator. However, the thick film capacitor fabricated by using the above-mentioned conventional dielectric paste has had problems as follows.
That is, there has been a problem that the size of a dielectric film obtained is inferior because the conventional dielectric paste contains a high amount of dielectric powder in order to obtain a high dielectric constant. It is necessary to sinter at a high temperature exceeding 900.degree. C. in order to complement the lack of the small size. However, sintering at such high temperature may exert an adverse effect on other circuit elements already formed on the substrate before the sintering, such as a capacitor electrode for the thick film capacitor already formed on the substrate. For instance, because the sintering temperature is 850.degree. C. to 900.degree. C. in general when the above-mentioned capacitor electrode is formed by way of baking, the capacitor electrode may undergo undesirable diffusion, reaction or the like when the dielectric paste is sintered in the temperature exceeding 900.degree. C. Therefore, it is desirable to be able to sinter the dielectric paste at as low a temperature as possible.